The present invention relates to a video data communication apparatus and method for communicating through a specified transmission route by converting an entered video data stream.
As a result of recent advancement in communication system using optical fibers, the communication capacity is expanded enormously, and systems for transmitting not only digital data used in computers, but also video signals, audio signals and other additional information by digitizing are being developed. For example, by employing an asynchronous transfer mode (ATM), high speed transmission using a network of 155 megabits/sec or higher is realized, and a video data communicating system on ATM is being put in practical use. The ATM is discussed and standardized in the ITU-T (International Telecommunication Union-Telecommunication Standardization Sector), and The ATM Forum and others, and many related publications are available.
Examples of transmitting video data of coding method of consumer-use digital VTR by ATM network are disclosed in xe2x80x9cDVC Nonlinear Editing System using ATM/WANxe2x80x9d at the annual meeting of Video Information Media Society, 1997, No. 23-5, xe2x80x9cMulticast/Real-time Transmission of DV/DVCPRO Data by ATM Networkxe2x80x9d at the winter meeting of Video Information Media Society, December 1997, No. 3-6, xe2x80x9cReal-time Transmission of DVCPRO50 Compressed Signals by ATM Networkxe2x80x9d at the meeting of Video Information Media Society, July 1998, and xe2x80x9cDVCPRO25/50 Transmission System over ATM and Fibre Channelxe2x80x9d at International Broadcasting Convention (IBC), November 1998, conference paper p. 567.
In this method, as the transmission protocol for putting the so-called DV-based signal compressed and coded by the DV system or DVCPRO system (the compression method mentioned in SMPTE Standard 314M) on the ATM cell, first, the TCP/IP protocol is utilized. In the TCP/IP, a greater buffer capacity than the buffer capacity for the processing time to re-send is needed in order to compensate for transmission errors on the network, and the delay is more than dozens of frames. As a result, while real-time communications between two parties are carried out in a long distance, sound and picture of the talk are delayed, and the communication is unnatural, and hence it has been demanded to shorten the delay time.
To decrease the delay, it is proposed to map DV-based signals directly in ATM layer without using TCP/IP protocol, and transmit by so-called Native ATM. For this purpose, the ATM adaptation type 1 (AAL1) or ATM adaptation type 5 (AAL5) is used. Since the AAL1 system has the transmission mechanism of clock information and forward error correction (FEC) mechanism, clock reproduction and error compensation of ATM network are possible at the reception side.
Therefore, the use of AAL1 is being started in the field of contribution relating to creation of contents for broadcasting, production and so on. At the present, however, the transmission apparatus using the AAL1 system is expensive, and the less expensive AAL5 transmission system is preferred in the general business field limited in the budget for communication system.
The AAL5 system is widely used in the field of computer network because the protocol process in the AAL layer is simple. For transmission of real-time AV signals using AAL5, the clock reproduction mechanism and error compensation mechanism must be added in the upper layer of the AAL5 layer, which is realized by the methods mentioned above.
In these conventional methods, however, only the DV-based signals can be transmitted by using the AAL1 or AAL5. For example, the stream transmitted in the SDTI system (SMPTE305M standard) enabling to transmit DV-based signal at 4-speed rate or transmit plural programs cannot be relayed by the ATM network by converting into ATM signal directly, that is, seamlessly without converting into other transmission format.
At the present, efforts of research and development are intensively concentrated on the high speed IP network of the next generation applying the WDM (wavelength division multiplex) technology and Next Generation Internet (NGI). It is demanded to adopt the high quality AV signals in the Internet protocol (IP) of which standard is being discussed at the IETF (Internet Engineering Task Force), that is, the present IPv4, or the IPv6 considered to be used widely in the future, but the present problems are that the DV-based signals or other high quality AV signals cannot be transmitted on the IP high speed network, IP over WDM or other next generation high speed key networks by formatting into IP packet, and that the received IP packet cannot be transmitted on the ATM network by converting directly into the ATM packet.
In the streaming using the AAL5 system, only by detecting the ATM cell loss or bit error at the reception side, it is a simple process of discarding the PDU (protocol data unit) including the error only, and the end-to-end transmission delay is small. On the other hand, when the PDU is discarded by error, the frame data to be reorganized by using the PDU is imperfect, and the video signal must be concealed, and the audio signal must be muted, so that the effect of the error must be limited to a minimum. That is, since the streaming using the AAL5 is small in delay and is suited to real-time live transmission, but not suited to contribution in which error-free information transmission is demanded.
The invention is devised in the light of the above problems, and it is hence an object thereof to present a video data communication apparatus capable of converting the SDTI signal or information transmitted in IP packet directly into the ATM packet, and further to present a video data communication apparatus capable of realizing both live transmission of low delay and error-free contribution by using the AAL5.
To achieve the object, the invention presents a video data communication apparatus comprising input means for entering a data stream including video data, header information extracting and combining means for extracting specified information from the header included in the input data stream, shuffling, and creating other header information, video data extracting and combining means for extracting video data included in the input data stream and arranging in specified sequence, and wrapper generating means for multiplexing the output of the header information extracting and combining means and the output of the video data extracting and combining means, and combining into one wrapper transmission block. In particular, the data stream to be entered is SDTI stream, IP packet data, or FC-AC stream of ANSI standard, and it is particularly effective if the video data to be transmitted as the payload of the data stream is data of DV system or DVCPRO system.
The invention further comprises receiving means for receiving a data stream and extracting video data, memory means for temporarily storing the extracted video data, error detecting means for detecting presence or absence of error of the extracted video data, error compensation means for compensating the error portion of the extracted video data, and error processing means for requesting re-send of at least part of the extracted video data, and correcting the error portion of the extracted video data stored in the memory means on the basis of the video data re-sent according to the request, in which the video data of which error is compensated by the error compensation means are issued as live output, and the video data of which error is corrected by the error correcting means are issued as contribution.
The live transmission output is low in delay because it is issued after error compensation process by referring to the reception data. The contribution output is free from error because the error portion is corrected according to the re-sent data. Therefore, a live image is displayed on a monitor, and video data free from error due to transmission can be recorded in a VTR.